The dyeing of graying hair is best done when the hair is just starting to turn gray so that the change of appearance does not become striking. The process of hair dyeing is rather messy especially for persons with dark hair. Most hair dyes are aniline-type compounds and the incidences of skin sensitization are the highest among such cosmetic preparations. More recently there are indications that some aniline type dyes may not be safe for general use.
There are several products on the market which have been described as effective for gradually coloring hair to a desired hue. These preparations are based upon the use of heavy metal salts, such as lead salts, in combination with sulfur, a sulfur precursor or a reducing agent. The coloring of hair by such products has two distinct advantages over hair dyes. Because of the slow darkening of the hair, the change of the appearance of a person is not noticeable. Secondly, unlike hair dye, such a preparation colors the growing hair from the root up and during use, the lower section of the hair does not appear white Hair grows approximately 1-3 mm. in 24 hrs. The clear demarkation of the dyed section and the growing section of the hair are often so striking that people must dye their hair again in a few days or weeks. For these reasons the gradual type of hair coloring preparations are popular.
Unfortunately however, the gradual-coloring hair preparations on the market today contain high percentages of lead salts, particularly lead acetate.
Lead is known to be poisonous and can cause mental retardation and even death. It has also been reported in the literature that soluble lead salt can penetrate through the skin. Yet such preparations are allowed to be marketed because of the high demand for their gradual coloring qualities.